An important commercial high nitrogen liquid fertilizer composition is one containing a mixture of ammonium nitrate and urea. For example, as taught in U.S. Pat. No. 3,746,528, ammonia is reacted with carbon dioxide, producing a urea plant reactor effluent containing significant amounts of the desired urea, as well as carbon dioxide, unreacted ammonia, and water. Generally, the unreacted ammonia is substantially vaporized off and "set" in an ammonium nitrate production plant. The urea solution then is admixed with aqueous ammonium nitrate to form a urea-ammonium nitrate solution.
Unfortunately, these high "N" containing fertilizer solutions have still had a slight undesirable ammonia content, and have exhibited unfortunately high salting out temperatures, such as 24.degree. to 26.degree. F., making them difficult to store and use in marginal temperature weather.
While such a so-produced urea solution is discussed as being "essentially ammonia-free", that "essentially" still is enough residual ammonia to spell trouble. The urea-ammonium nitrate solution resulting thus contains a small but an undesirable concentration, usually about 0.2 to 0.4 weight percent, of free ammonia. The residual free ammonia in the urea/ammonium nitrate solution is objectionable, since application of this fertilizer solution tends to cause, for example, a "burning" effect on young wheat plants.
In some instances, the ammonia-containing urea/ammonium nitrate solution has been treated wih nitric acid at such as 225.degree. F. to 235.degree. F. (107.degree. C. to 113.degree. C.) to reduce the residual ammonia. This, I find, results in some loss (reversion) of the urea.
U.S. Pat. No. 3,746,528 treats the urea production effluent containing carbon dioxide, unreacted ammonia, as well as water, and urea, in a neutralization zone with nitric acid at a relatively high temperature of about 257.degree. to 347.degree. F. (125.degree. to 175.degree. C.) and works to control the pH above about 6.5 to help avoid hydrolysis of the urea. This process provides a direct reaction/neutralization of the high ammonia content of the raw urea production effluent, resulting in an aqueous admixture of urea/ammonium nitrate.
However, such high temperature treatment is counterproductive. Some of the very valuable urea is lost by reversion back to ammonia and carbon dioxide which, obviously, is counterproductive.